The present invention relates generally to washing machines, and more particularly to a washing machine which includes an off-axis variable speed motor coupled to an agitator and a basket.
Conventional washing machines typically include a basket that holds articles such as clothes to be washed, an agitator disposed within the basket which agitates the clothes in the basket, and a motor which drives the agitator and the basket. The motor is typically an AC induction motor, which can reverse its rotation direction to achieve different modes in the wash cycle. The motor, for example, may rotate in a first direction during the agitation mode and a second direction, opposite the first direction, in the spin mode. A transmission is provided with gears to convert the rotary motion of the motor into oscillatory motion of the agitator during agitation, or high speed rotation during the spin mode. In addition, associated with a typical transmission are a brake to hold the transmission (and hence the basket) immobile during agitation mode and a clutch or actuator to engage or disengage the brake. An additional slip clutch is typically installed between the motor and the agitator, since the induction motor typically cannot immediately generate the full torque required.
Although washing machines powered by AC induction motors generally operate in a satisfactory manner, they are generally both complicated and inflexible. For example, the transmission is a relatively complex unit that includes many moving parts and contributes substantially to the reliability and cost of the washing machine. It is also configured to provide only a limited number of options with regard to the motion of the basket and agitator.
To overcome some of the limitations of conventional AC induction motor powered washing machines, variable speed reversible electric motors have been implemented to simplify the construction of washing machines and to allow more flexibility in controlling the motion of the basket and agitator. For example, U.S. Pat. No. 4,813,248 issued Mar. 21, 1989 to Smith et al. discloses a washing machine that includes a three-phase electronically commutated motor (3.phi. ECM) which directly drives the agitator and basket. The rotational speed and direction of the 3.phi. ECM can be controlled with electronic commutation equipment which enables the 3.phi. ECM to move in a clockwise and counterclockwise motion causing the agitator to be oscillated clockwise and counterclockwise in agitation mode. The electronic commutation equipment also drives the motor continuously in spin mode to spin the agitator and basket.
Although the Smith et al. apparatus has certain advantages over prior AC induction motor powered washing machines, it also has several disadvantages. For example, the direct drive arrangement, in which the 3.phi. ECM is arranged on the same axis of rotation as the basket and agitator, results in the transmission of torque ripple vibrations from the 3.phi. ECM to the tub, basket, agitator, and other parts of the washing machine. The transmission of torque ripple through the direct drive arrangement generates a significant amount of noise, which is an undesirable feature in a washing machine. Torque ripple also has adverse effects on other components of the washing machine, which are vibrated during use and thus may be fatigued. The effects of torque ripple are augmented by the low frequency at which the motor is operated, which frequency often coincides with the natural oscillating frequency of the washing machine or its subsystems. Thus, the transmission of vibrations and noise from the 3.phi. ECM to other components of the washing machine is, unfortunately, very efficient.
In addition, the placement of the 3.phi. ECM directly below the agitator and basket introduces significant constraints with respect to the design of the 3.phi. ECM. There is a limited amount of space under the agitator and basket due to the desire to provide a large basket while keeping the height of the washing machine at a comfortable level. Thus, the 3.phi. ECM must be designed to have a relatively small height and a large number of poles, which adds to the cost of the washing machine.
It would be desirable, therefore, to have a washing machine that provided the flexibility of a variable speed reversible electric motor, for example, while avoiding the problems of known variable speed motor powered washing machines.